1. Field of the Invention
The present invention generally relates to image processing systems and more particularly relates to a method and apparatus for providing scanned images from a portable 2-D scanner.
2. Description of the Related Art
There are many applications that need optical scanners to convert paper-based objects, such as texts and graphics, to an electronic format that can be subsequently analyzed, distributed and archived. One of the most popular optical scanners is flatbed scanners that convert scanning objects, including pictures and papers, to images that can be used, for example, for building World Wide Web pages and optical character recognition. Another popular optical scanner is what is called sheet-fed scanners that are small and unobtrusive enough to sit between a keyboard and a computer monitor or integrated into a keyboard to provide a handy scanning means. Nearly all of the scanners are scrolling types, namely a scanner and a scanning document must move against each other in order to scan the entire scanning document. Typically, this type of scanner uses a one-dimensional linear sensor to sense the entire scanning document. Further the trend of the scanner design is getting smaller and more portable.
With the increasing popularity of portable computing devices, such as personal data assistants (PDA), there is an emerging need for scanners that should be even smaller or simply integrated within a portable computing device. One of the exemplary portable computing devices may be a Palm Pilot from 3Com, Inc., it would be great convenience if the Palm Pilot is equipped with a scanning capability so that a user of a Palm Pilot can scan in a document in various working conditions.
Nevertheless, a document has a certain size, for example 8 by 11.5 inches in compliance with the US standard paper size. To scan in such document, the scrolling type scanners could not be designed smaller than the width of a scanning document. The past efforts have been focused on two-dimensional image sensors. For example a digital camera that can be designed much smaller than a document may be used to image the document. The digital camera uses a two-dimensional image sensor to take a snapshot of a scene. However, the resolution requirement for a scanned image is generally of quite high, typically from 300 to 600 dot-per-inch (dpi). Thus the two-dimensional image sensor in the digital camera has to be tremendously high, which becomes a major factor in the cost of such image sensor. As a result, using digital cameras for scanning documents is not yet popular.
There is therefore a need for solutions that can render a digital camera with a regular image sensor suitable for document scanning while providing high resolution images.
The present invention has been made in consideration of the above described problems and needs and has particular applications to scanners using 2-dimensional image sensors. Traditionally, a scanner could not be designed smaller than a width of a document as the document has to be scanned across for a good image resolution. When using a digital camera to take a snapshot of the document, the result image resolution is often too low to be a practical useful image. With the present invention, the digital camera can be used to provide a scanned image with high resolution. Further scanners employing the present invention can be designed as small as a palm size or integrated with many portable devices such as a Palm Pilot or a cellular phone.
According to one aspect of the present invention, a series of images are successively generated from a sensing module in a scanner as the scanner is moving across a scanning document. A first image is initially kept in a memory. When a second image becomes available, an overlapping between the first image and the second image is located. From the overlapping, it is to determine if the stored first image is precisely registered with the second image or vice verser. If the two images are completely registered, a signal-to-noise enhanced image or an image of better resolution is obtained by averaging the two images or an interpolation process. If the two images are not registered, an combined image is obtained by first rescalling one of the images accordingly and followed by combining the two images (one of which is rescaled). Either the signal-to-noise enhanced image or the enlarged/combined image is then stored in the memory to work with a next image. The process is repeated till all the images are processed. As a result, a combined or an enlarged image representing the entire document is produced.
The present invention may be implemented in numerous ways including a method, a computer readable medium, a system, or an apparatus, each yields one or more of the following benefits and advantages. One of them is the possibility of introducing a scanner much smaller than a document while still producing scanned images of high resolution and quality. Another one is a soft scanner that can be loaded in any computers equipped with a camera. Working along with the soft scanner, the camera provides a necessary means to provide images to the soft scanner that subsequently produces scanned images.
Other objects, benefits and advantages together with the foregoing are attained in the exercise of the invention in the following description and resulting in the embodiment illustrated in the accompanying drawings.